Silent linear switches are the quietest. If that's not an option, then linear switches with o-rings.
Also you frequently get quite a lot of noise from the stabilizers on the large keys. Your only real option there is to lube them, but that's not really feasible on most off the shelf keyboards.
Very quickly my coworkers encouraged me to buy one with silent clear switches.
I now own two.
The clicky one stays at home.